Access terminals, such as laptop computers, personal digital assistant devices, mobile or cellular phones, personal media players, or other devices with a processor, that communicate through wireless signals are becoming increasingly popular and are used more frequently. Many access terminals are adapted to communicate via Wireless Local Area Networks (WLAN), and several emerging wireless communications standards have been developed and are being developed for facilitating such WLANs.
The Institute of Electronics and Electrical Engineers (IEEE) has developed various WLAN standards (or revisions) under the umbrella of its IEEE 802.11 standard. IEEE 802.11 denotes a set of WLAN air interface standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters). Such WLAN networks are often referred to as “WiFi” or “wi-fi” networks and allow electronic devices to communication wirelessly (e.g., exchange data, access other networks, etc.).
However, the available frequency spectrum for such wireless networks is quite limited and there is an ever increasing need for bandwidth demanded by wireless communications systems. As such, reuse of, and/or co-existence with, existing frequency spectrum allocations is desirable. One relatively recent development corresponds to implementing a WLAN using white space (also referred to as whitespace). “White space” may refer to radio frequencies allocated to a broadcasting service but not used locally (e.g., within short range). In the U.S., the Federal Communication Commission (FCC) Report and Order (R&O) recently opened up an opportunity of unlicensed usage of the white space. Use of white space for implementing a WLAN according to the IEEE 802.11 standard is being developed under an amendment to the IEEE 802.11 referred to as IEEE 802.11af. “White-fi” is a term being used to describe the use of a Wi-Fi technology within the TV unused spectrum, or TV white space. Television channels have typical bandwidths of 5 MHz in the U.S., but bandwidths may be different (e.g., 6 MHz, etc.) in other countries.
The specification of IEEE 802.11af proposes “clocking down” an 802.11n 20 MHz signal by different factors for different bandwidths (BWs). Such a design expands cyclic prefix (CP) length and symbol duration by a down clocking factor, for example by a factor of 4 (to 3.2 μs) in 5 MHz transmissions. Such design may raise various issues. First, such a design may present provisions for much greater delay spreads only in 5 MHz mode. A large delay tolerance may be needed for 10 and 20 MHz modes too due to larger range if TV White Space (TVWS) signals. Secondly, co-existence of different BW devices within a basic service set (BSS) may not be supported. For example, a 5 MHz device may not be able to decode a preamble of a 10 MHz transmission since the symbol durations are different. Thirdly, overlapping basic service set (OBSS) co-existence may not be supported.
Consequently, there is a need for solutions that permit the co-existence wi-fi transmissions in television white space.